Over time and through repeated use, bones and joints can become damaged or worn. For example, repetitive strain on bones and joints (e.g., through athletic activity), traumatic events, and certain diseases (e.g., arthritis) can cause cartilage in joint areas, for example, which normally provides a cushioning effect, to wear down. When the cartilage wears down, fluid can accumulate in the joint areas, resulting in pain, stiffness, and decreased mobility. The same can happen in the case where tendons in a joint become lax or soft tissues in or adjacent the joint tear become damaged or worn.
Arthroplasty procedures can be used to repair damaged joints. During a typical arthroplasty procedure, an arthritic or otherwise dysfunctional joint can be remodeled or realigned, or an implant or implants can be implanted into the damaged region. Arthroplasty procedures may take place in any of a number of different regions of the body, such as a knee, a hip, a shoulder, or an elbow.
One type of arthroplasty procedure is a shoulder arthroplasty, in which a damaged shoulder joint is replaced with prosthetic implants. The shoulder joint may have been damaged by, for example, arthritis (e.g., severe osteoarthritis or degenerative arthritis), trauma, or a rare destructive joint disease.
Implants that are implanted into a damaged region may provide support and structure to the damaged region, and may help to restore the damaged region, thereby enhancing its functionality. Prior to implantation of an implant in a damaged region, the damaged region may be prepared to receive the implant. In the case of a shoulder arthroplasty procedure, one or more of the bones in the shoulder area, such as the humerus and/or glenoid, may be treated (e.g., cut, drilled, reamed, and/or resurfaced) to provide one or more surfaces that can align with the implant and thereby accommodate the implant. Standard alignment instrumentation may be used for locating a position and orientation to resect the humeral head for proper humeral stem placement in the humerus.
Accuracy in implant alignment is an important factor to the success of the procedure. A one to two millimeter translational misalignment, or a one to two degree rotational misalignment, may result in imbalanced ligaments, and may thereby significantly affect the outcome of the procedure. For example, implant misalignment may result in intolerable post-surgery pain, and also may prevent the patient from having proper deltoid tension or range of motion.
To achieve accurate implant alignment, prior to treating (e.g., cutting, drilling, reaming, and/or resurfacing) any regions of a bone, it is important to correctly determine the location at which the treatment will take place and how the treatment will be oriented. Currently available instrument and tools do not always enable the surgeon to make the most accurate cuts on the bone surface in preparing the target joint for implantation. Thus, there remains a need for tools that improve the accuracy of the joint resurfacing process.